I'd say she was in her mid 60s, but its sometimes difficult to tell ages in these older pictures. Hardship ages faces, and our ancestors certainly had their fair share of those!
I don't think she looks stern, though. Looks to me like there's a glint in her eyes of a slightly mischievous character, and looks like she'd have been a sweet old lady.
Shouldn't take much to clean her picture up, but I'm stuck at work with no photo software. Bah!
Glen